1. Field of the Invention
The subject invention relates to dies used to form tubular twist beam parts, and methods of forming tubular twist beam parts.
2. Related Art
Automotive vehicles include twist beam axles, also referred to as twist beam parts or twist axle parts, for connecting control arms in a twist suspension system. A twist beam axle extends between rear wheels of the vehicle and provides a means of packaging the suspension while minimizing intrusion into the passenger compartment. The twist beam axle may comprise an H-shaped, C-shaped, U-shaped, or V-shaped bar formed of a metal material.
The twist beam axle may also comprise a tubular twist beam part, which is formed by pressing or molding a tube into a predetermined shape. The tubular twist beam part is not only a structural member, but also acts as a torsion spring. An example of a tubular twist beam part is disclosed in U.S. Patent Application Publication No. 2010/0301577. The weight of the tubular twist beam part is preferably low since it contributes to the total weight of the automotive vehicle. However, tubular twist beam parts experience a significant amount stress due to twisting and other factors. Therefore, maximum stress levels, especially those due to twisting, dictate the material thickness and the weight of the tubular twist beam part.
The tubular twist beam part is also used to control a roll rate of the vehicle, which affects the ride and handling of the vehicle. The roll rate is analogous to a vehicle's ride rate, but for actions that include lateral accelerations, causing a vehicle's sprung mass to roll. Roll rate is expressed as torque per degree of roll of the vehicle sprung mass, and is typically measured in Nm/degree. The roll rate of a vehicle does not change the total amount of weight transfer on the vehicle, but shifts the speed at which and percentage of weight transferred on a particular axle to another axle through the vehicle chassis. Generally, the higher the roll rate on an axle of a vehicle, the faster and higher percentage the weight transfer on that axle. A slower weight transfer reduces the likelihood of vehicle rollover conditions. The dimensions and design of the tubular twist beam part have a significant influence on the roll rate of the vehicle.
The tubular twist beam parts are formed using dies and other tools. Oftentimes, multiple dies or tools and three separate forming steps are needed to form a tubular twist beam part with dimensions providing the desired roll rate, which is costly and time consuming. In order to achieve a new roll rate, or to “tune” the roll rate of a particular part, the die or tools must be re-designed, which is costly and may take weeks or months. Further, to manufacture multiple parts each providing a different roll rate, different dies and tools must be designed and employed, which is also costly and time consuming.